This invention relates generally to color display devices and particularly to an arrangement for the cells within the pixels of a color alpha-numeric and graphic display device.
In color display devices each pixel of the display includes cells which individually emit the red, green and blue primary colors of light. The pixels are arranged in rows substantially parallel to a horizontal axis and in columns substantially parallel to a vertical axis. For alpha-numeric and graphic display devices, the pixels are comprised of bilevel cells whereby actuated cells provide light and unactuated cells provide no light. The desired alpha-numeric and graphic displays are produced by selectively actuating the cells required to produce the desired display. Displays having one of the three primary colors are produced simply by actuating the desired color cells within the pixels needed to produce the desired pattern. For example, when a green display is desired, the green cells within the pixels needed to produce the desired pattern are actuated, while the other cells within the pixels remain unactuated. White is produced by simultaneously actuating all three color cells within each pixel, and black, or nearly black is produced when none of the cells within a pixel are actuated. Other colors are produced by simultaneously actuating the cells required to produce such color. For example, magenta is produced by simultaneously actuating the red and blue cells.
Alpha-numeric and graphic display devices require horizontal, vertical and diagonal straight lines. Accordingly, the pixels are arranged horizontally and vertically in rows and columns in an effort to produce such lines. However, when each pixel is composed of three cells, the cells are typically arranged in a triangular pattern and all three cells cannot be vertically or horizontally aligned and straight lines can not be produced. It has been found that the appearance of alpha-numeric and graphic displays can be improved by adding a fourth cell to each pixel to provide diagonal symmetry to the pixels. However, problems nevertheless arise because the color of the additional cell upsets the color balance of the pixel. Additionally, all four cells within a pixel can not be horizontally or vertically aligned and therefore the production of some colors of displays requires the selection of unaligned cells within the pixels and straight lines extending in all directions can not be produced. Because of these difficulties, there is a need for an arrangement of the cells within the pixels which yields alpha-numeric characters, and line segments which are the easiest to read and which are the most pleasing to a viewer situated at the normal viewing distance. An acceptable alpha-numeric display device must meet several criteria for the straight and diagonal line segments which form the characters and graphic portions of the display. When viewed from the standard viewing distance, upwardly and downwardly sloping diagonal lines should have the same general overall appearance. Also, horizontal and vertical lines should appear straight. These criteria must be met for all colors of alpha-numeric displays. The present invention is directed to arrangements of the cells within the pixels of a display device which meet these criteria.